1. Field of the Invention
The present invention relates to an assembly of donor and receiver detonating cords and a detonation-transmitting device which joins said cords in detonation-propagating relationship, and to a connector for holding donor and receiver detonating cords in detonation-propagating relationship to the input and output ends of a detonator.
2. Description of the Prior Art
Detonating cords are used in non-electric blasting systems to convey or conduct a detonation wave to an explosive charge in a borehole from a remote area. One type of detonating cord, known as low-energy detonating cord (LEDC), has an explosive core loading of only about 0.1 to 2 grams per meter of cord length. Such a cord is characterized by low brisance and the production of little noise, and therefore is particularly suited for use as a trunkline in cases where noise has to be kept to a minimum, and as a downline for the bottom-hole priming of an explosive charge.
In blasting practice, detonating cords must be joined together, e.g., in the joining of downlines to a trunkline, and the explosion must be transmitted from one cord to another. Depending on its structure and composition, a low-energy receiver cord may or may not be able to "pick-up", i.e., to detonate, from the detonation of a donor cord with which it is spliced or knotted. If the receiver cord is unable to pick up from the detonation of the donor cord, a booster or starter such as that described in U.S. Pat. No. 4,248,152 can be introduced between the cords. This particular booster contains a granular explosive charge, e.g., PETN, between the walls and closed bottoms of inner and outer shells, one cord being held in an axial cavity in the inner shell in a manner such that an end-portion of the cord is surrounded by the booster explosive, and another cord being positioned transversely outside and adjacent to the closed end of the outer shell. One of the cords (donor) initiates the booster explosive and this in turn initiates the other cord (receiver), which usually is LEDC. The axial cord has its end, i.e., its explosive core, near, and preferably in contact with, the inner shell adjacent to the booster explosive charge, a cord-gripping means being required to hold the axial cord in this position. Thus, this booster transmits a detonation to the end of a detonating cord from the side of a detonating cord, or vice versa, and is especially suited for trunkline/downline connections.
In the art of delay blasting, a delay unit or device is inserted between two lengths of a detonating cord trunkline, or between a trunkline and downline to cause a surface delay of the detonation of an explosive charge in a borehole. A connector for securing a high-energy detonating cord (HEDC) such as Primacord.RTM. to each end of a delay device is described in U.S. Pat. No. 3,349,706. This connector is adapted to hold a U-shaped segment of the cord adjacent to each end of the tubular shell of a delay unit located in the bore of a central tubular portion whereby the side-output of one cord segment initiates the delay unit, and the latter in turn initiates the other cord segment through its side wall.
Certain low-energy detonating cords, especially the cord described in U.S. Pat. No. 4,232,606, are known to be difficult to initiate by means of a detonator if the detonator-to-cord abutment is not coaxial, and although the booster described in the aforementioned U.S. Pat. No. 4,248,152 is capable of initiating said cord through the cord side wall, the initiation of a cord of this type by a detonator having its base-charge end butted against the side wall of the cord has not been reported. For example, of the delay connectors described in U.S. Pat. No. 3,306,201, the one which is designed to be side-actuated by, and to side-initiate, a detonating cord, requires a high-energy detonating cord, e.g., one having an explosive loading of 16 grams per meter. LEDC donor and receptor cords are positioned coaxial to the delay device in the connector, i.e., with the cord ends abutting the delay device. Co-pending U.S. patent application Ser. No. 144,535, filed Apr. 28, 1980, now U.S. Pat. No. 4,299,167, describes an initiator for introducing a delay between two lengths of LEDC trunkline or an LEDC trunkline and LEDC downline. Although this surface delay initiator is actuated from the side output of the donor cord, the receiver cord which it initiates is end-initiated, i.e., the receiver cord coaxially abuts the initiator. Coaxial positioning of a cord may be a disadvantage because the cord has to be cut to provide the required abutting end surface, i.e., cord continuity is lost.
U.S. Pat. No. 3,709,149 describes a delay detonator which is initiated by a low-energy detonating cord positioned laterally adjacent an ignition capsule in the detonator. However, this detonator generally is positioned in a booster unit embedded in an explosive charge in the borehole. When used at the surface to connect a trunkline to one or more downlines, the downlines abut the side of the detonator shell at the base charge end.